Draft: Graphical plot of yMMSL configuration

[DaanVanVugt]

The idea is to have a nice method to visualize the workflow you are developing.
For this a new command is defined

muscle3 graph file.ymmsl

See --help for an up-to-date description of the options.

Things to do still

• Provide documentation
• See if we can make the arrows 'feel' more in the direction of data flow
• More distinct styling (thick lines, like MMSL docs? different colors for stateful / stateless actors?)
• Show implementation name
• Investigate hovering for more details (should work in svg)
• Compare a few layout engines (needs example cases)
• Plot unconnected ports (optional)
• Investigate options for live-updating (show running, waiting models, message counts)